1. Field of the Invention
The present invention relates to a pencil lead that includes an organic-inorganic hybrid resin in fine pores in a porous lead body.
2. Description of the Prior Art
Pencil leads are broadly divided into black leads having graphite as a main component, and colored leads in which a pigment or dye is added to a filler as a colorant. The black leads undergo a sintering process during the manufacturing process, and some of the colored leads are sometimes manufactured by a similar sintering process. Pencil leads manufactured by such sintering processes exhibit a porous structure having countless fine pores.
In most cases, colored leads (so-called colored pencil leads) manufactured by sintering are first manufactured as an initially white or pale-colored porous lead body, and then a dye ink is caused to impregnate the fine pores of the lead body. In the invention disclosed in JP 2015-160887 A, a resin is filled into fine pores in order to strengthen the lead body.
Note that colored pencil leads formed with fine pores can also be manufactured without undergoing a sintering process (Japanese Pat. Nos. 2641810 and 2726198, and JP H07-126568 A and JP 2000-26785). Technology has been described in which, in order to prevent degradation over time due to moisture absorption, the surface of such an unsintered colored pencil lead is coated with an organic-inorganic hybrid material to form a moisture-proof film (JP 2002-348516 A).
The organic-inorganic hybrid material described in JP 2002-348516 A is described as a “formulation of an inorganic material and an organic material”, “especially those in which mixing occurs on the nanoscale, and sometimes on the molecular scale”. Such organic-inorganic hybrid materials have the characteristic of being “excellent in mechanical strength and high heat tolerance while being flexible like plastics” (see “Organic-Inorganic Nano-Hybrid Materials” by Yoshiki CHUJO, The Micromeritics, Hosokawa Powder Technology Research Institute Co., Ltd., Oct. 30, 2006, No. 50, p. 11-p. 15).
The present invention concerns further increasing the mechanical strength of a pencil lead by incorporating an organic-inorganic hybrid resin having these characteristics into fine pores of a pencil lead that exhibits porous structure, irrespective of whether the lead is a black lead or a colored lead.